The Effect of Clinch™ on Ants Common to Northern California Almond Orchards

Holly Johnson CSU, Chico, College of Agriculture

Abstract

For a variety of reasons ants are becoming a severe pest in California almond orchards, including warmer winter temperatures in recent years, and a change in cultural practices. Ant damage to the crop can exceed 20% in susceptible cultivars. Many current methods of ant control are not a viable solution for long term control. Clinch™ is a recently registered insecticide for use in almonds with the potential to reduce ant populations. In this study it was found that Clinch™ significantly reduced the number of ants present in plots compared to an untreated control in a Northern California almond orchard 163 days after treatment (p=.0783). This study suggests that Clinch™ may be a viable method of long term ant control.

Introduction

Until recently, ants were a minor almond pest in California. However, ants are becoming a more severe pest as a consequence of changing orchard practices. Practices such as substituting nontillage for tillage orchard floor management, drip or micro sprinklers for flood irrigation and the switch to IPM controls for navel orange worm control (“Hit”, 1999). Also, growers leave nuts on the orchard floor longer for drying which leads to increased ant damage (Reil et al., 1982). Ants damage nuts by feeding on the kernel (Zalom et al., 1985). Ant damage can exceed 20% in susceptible cultivars resulting in a substantial loss in profit (Darby, 2000).

Species that cause most of the damage are the pavement ant (Tetramerium caespitum) and the southern fire ant (Solenopsis xyloni). The fire ant has the widest distribution and causes the most problems in orchards (Reil et al., 1982). Chemical spray applications such as Lorsban have been shown to give only temporary control. These chemicals can kill nontarget insects including beneficials and mites (Reil et al., 1982). Abamectin, the active ingredient in Clinch™ is a stomach insecticide that kills ant slowly after it is ingested and it also interrupts the reproductive cycle, leaving the queen unable to lay viable eggs ("Hit," 1999). Fire ants do not rapidly recolonize abamectin treated soils, so Clinch™ insecticide may eradicate the fire ants and may also delay, or prevent their reinfestation (Campbell, 1989).

The objectives of this experiment are to determine if Clinch™ is a viable method of long term ant control, and determine the effects of Clinch™ on beneficial and economically harmful ants.

Materials and Method

A nine-year-old 29-acre, drip irrigated almond orchard, planted on a 20' x 18' spacing with a mixed clover cover crop located in Arbuckle was selected for the experiment. Samples taken September 26th identified the types of ants present. Samples also showed that ant distribution was fairly uniform throughout the orchard. A buffer of four trees to prevent ants from other plots eating the bait separated each plot. There were sixteen plots of 8 trees by 8 trees (26,010 square feet). Plots were randomly assigned to as an untreated control, or treatment of Clinch™ at the recommended rate of 1 lb. per acre.

Ants were sampled two weeks prior to treatment, and after the ants became active in the spring 163 days post treatment. All plots had five vials with hot dogs in them for bait. Hot dogs will attract both beneficial and economically harmful ants, providing an estimate of the number of ants present. Hot dog vials were placed in the plots for one hour, then capped, and frozen. The ants in the vials were then counted, species identified, and the total ants and total harmful ants were analyzed. Data was analyzed using Analysis of Covariance, with initial sample counts used as the covariant and a .08 level of significance.

Results

Treatments were shown to have a significant effect for total harmful ants (p-value of .0752). See Table 1 for ant counts. Treatments also significantly reduced the number of total ants (p-value of .0783). See Table 2 for counts.

Discussion

This study resulted in a significant reduction in ant populations with the use of Clinch™. Results indicate that Clinch™ significantly reduced ant populations in the plots at over a period of 163 days. Therefore, this study could suggest that Clinch™ might be a viable method of inexpensive long-term ant control. Although Clinch™ had the same effect on both beneficial and harmful ants, it is advisable to use it if there is a significant number of harmful ants in the area to be treated because of the potential loss of income.

By using estimated 1999-2000 crop yields of 1,730 lbs./acre and a projected price of $1.36/lb (Adu-Asamoah, 1999) the projected savings resulting from the use of Clinch™ follows. Clinch costs $11.80/acre, and has minor application costs. At a 10% reduction in ant damage $223.45/acre could be saved. At only a 1-% reduction in ant damage $11.55/acre could still be saved. This study suggests that Clinch™ is an inexpensive method of long term (month’s) ant control that offers great benefits.

Future studies should be conducted to determine how immediately a reduction in ant activity occurs, what application intervals are necessary for longer term control, if there is a corresponding reduction in damage to nuts at harvest and how long the kill lasts.